Electric music transmission



Dec. 29, 1936. V N RGO ET AL 2,065,774

ELECTRIC MUSIC TRANSMISSION Filed Aug. 22, 1951 TO SOUND REPRODUCERv INVENTOR ozone vou A zco & FRITZ scuaoran AT OR Y Patented 2%, Edit Drahtlose Telegraphic in. b. R, Berlin, Ger many, a corporation of Germany Application August 22, N31, Serial No, 5583M In Germany September 2, 1930 @iaims.

The present invention is based upon and is intended to improve upon the method of sound generation, The timbre of any soundfis governed by what may be called resonance formants. These so-called resonant iormants" are damped oscillations which are excited by a series or sequence of impulses governing the fundamental pitch or note, and which decay inside one period of the fundamental. The pitch, the initial amplitude, and the damping of the said formants impart to and impress upon the sound its characteristic vocal or instrumental timbre or hue, as it were.

Circuit arrangements for the purpose of producing the said formants of the fundamental note by electrical means inside a tone frequency regenerative oscillation circuit by the aid of exciting the same by a glow-discharge interrupter" or equivalent means have already been suggested. Reference to this work may be found in the publication "Elektrische Musik" by Dr. Ing. Friedrich Trautwein, published in 1930 by Weidmannsche Buchhandlung, Berlin S. W. 68, Germany. The frequency and amplitude of such a glow-discharge lamp-circuit are controlled by way of an amplifier tube and, for example, by a manual control through the use of a variable resistance. By the tuning and the variable gain of the formant circuit, it is feasible to generate sounds of widely different characteristics with. the result that the peculiarities inherent in various instruments can be imitated by electrical means and methods.

The present invention aims to use the abov outlined basic idea for improving and raising, from an economic viewpoint, the condition of transmission oi music both in broadcasting as well as iocai sound reproduction by means of wire, similar devices.

of the invention, ad the fact that the exampie, may i" is called upon ".ency range, and to in" e sounds by the overtones recuired use of such ways and in combination with s ducer The latter, whether c nsisting of a broadcast receiver set, a sound. rep ducing device of an electric phonograph operated with disk records, sound. film, steel-wire, etc, tor stor ing up the sound, thus contains the parts of a scheme adapted to excite one or more formants (or as it were, cause the operation of several reg= (Clo 179 m isters) by the agency of such fundamentals as have been transmitted from the transmitter or broadcast station or derived from the sound record. By the variable and "dosable composition of the resonance formants, the desired timbres are producible synthetically. It is thus made possible in broadcast reception to vary Widely the transmitted music in accordance with personal tastes, both as regards character and expression. The same situation holds true of local reproduction of stored or recorded music i from a sound record of some sort.

According to this invention the side-frequency bands of the broadcast waves may be limited to substantially only the fundamentals of the sounds without the resonance formants having higher frequencies, or it is possible at any rate to tune the receiver apparatus more selectively inasmuch as the dosing or regulating in volume and number of the resonance formants is accomplished only in the receiver set. The same sort of saving is secured in recording the original sound upon the sound record or support. The apparatus used for the recording as well as the carrier of the records are, therefore, not required to fulfill such high demands as regards the reproduction of the highest frequencies as heretofore.

It is moreover feasible to control automatically the selection and the dosing" of the various registers, that is, of the resonance formant circuits in the reproducer apparatus. For this purpose, for instance, in broadcast work, recourse could be had to distinct irequencies which are brought to act upon control relays of the receiver responsive thereto. it is, however, also feasible to em ploy at the receiver and simple synchronous switches, e. cloclrivorks which are allowed to ion down the same rate or rhythm as cram or piece transmitted from the station so that they ll ti of the registers. "in the case oi stereo apart from the sounctcarrier proper,

utilize distinct con'""ol dia to connect and disconnect the various the de ti sense. This control. on another clockwork synciirc l the mover oi soundmarrie" it though is also possible to combine 1;

sonically the record carrier, ior ancby forming another track or groove aio tracts containing the acoustic records. Li.

instance the second track is intended to actuate the registers. Instead of the alcove means the suriace oi the sound record or may have variations of color by presenting light and dark contrasts whereby the selection of the proper registers can be insured photo-electrically by the aid of a small light-source and a photo-electric cell.

In the case of broadcast transmission the at-.

tempt to transmit the current curve suited for the shock excitation of the resonance formant circuit or circuits in the receiver apparatus conjointly with the modulation of the carrier wave is attended with difficulties. Inasmuch as the said current curve contains periodic irregularities or discontinuities so that there are overtones of the fundamental wave alongside the latter, a very wide frequency channel would be required therefor, and this would militate against the very aim of this invention in which the channel is to be narrow in the sense of this invention. In order to obviate this difliculty the shape of current curve as required for shock excitation is produced in the local receiver apparatus. Hence, the fundamental frequency is transmitted in the shape of a sinuous note which is as pure as possible, and the latter controls in the receiver set, for example, by causing distortion of the plate current of a thermionic tube or, better still, by acting upon a trigger (tilting) oscillation scheme in the plate circuit, the abruptly intermittent discharge occurring at like frequency which is required for the excitation of the resonance formant circuit.

One embodiment of this scheme is illustrated by way of example in the accompanying drawing, where i denotes the antenna of a broadcast receiver, 2 the tunedgrid circuit of the audion tube 3 wherein demodulation is insured and whose audio frequency energy serves to control in the plate circuit the trigger oscillation scheme comprising the glow-discharge or gaseous-conduction lamp 4 and paralleled connected condenserelement 5. The circuit arrangement so far described acts by way of the transformer 6 upon the grid of a tube 1. Coupled with the plate circuit of tube '1 is the tuned audio frequency resonanceformant circuit 9, including a capacity element ill and an inductance i i which is made regenerative by the provision of the condenser 8. By the excitation of the damped oscillation of this circuit 8 the timbre of the sound is governed by virtue of whether the gain is chosen greater or smaller. However, inside the scope of this invention a plurality of such differently tunable circuits 9 may be provided with the end in view to make the timbre still richer and more variegated.

The received impulses are transferred from the antenna 5 to the tuned circuit 2 of the receiver and the signals are detected by means of the grid leak and condenser and cooperating with the tube 3. it will be readily appreciated that the incoming rectified signals of which the sound reproduction is desired, will serve to trigger the neon lamp d since the voltage which charges the condenser 5 and across which the neon lamp 4 is connected, will suddenly rise when the incoming signal drives the grid in the positive direction to lower the impedance of the tube 3. This permits the condenser to reach the break-down voltage of the lamp 4 which time the glow discharge commences and discharges the condenser 5. This induces, by way of the transformer connected in the anode circuit of the tube 3, a sharp impulse to actuate the grid of the tube 1. The transformer connected in the anode of the tube 1 induces a very sharp impulse in tum into the resonant circuit 9, comprising the inductance ii and condenser l0. Accordingly, therefore, there will result, due to the resonant characteristics of the circuit, oscillations which will be damped out very rapidly, and these oscillations will resemble in form those produced by a spark transmitter, formerly used in radio communications. These impulses will comprise damped oscillations, the frequency of which is known as the wave frequency and the number of impulses per second gives rise to what is known as the group frequency. The group frequency, of course, is determined by the frequency of the incoming detected signals. Positive feed-back is fed from the tuned circuit 9 to the grid of the tube 1, by means of variable condenser 8 and it will be appreciated that the feed-back will, accordingly, be a linear function of the frequency. That is to say, that the amount of energy fed back to the grid of the tube I will be proportional to the frequency, and accordingly, therefore, the higher components of frequencies present due to the damped oscillations in the tuned circuit 9 will serve to actuate the grid of the tube 1 to a greater extent than the lower frequencies. This has the effect of essentially increasing the gain of the higher frequencies, so that the tuned circuit 9, acting in conjunction with the feed-back condenser 8, serves to give a band-pass filter effect, in which the desired range of frequencies are transmitted with uniform amplitude. This comes about from the fact that while the response curve of the tuned circuit is normally peaked, due to the fact that the higher frequencies are amplified to a greater extent than the lower frequencies, the over-all response of the system which feeds the sound reproducer tube, will not be peaked, but will be rather fiat, since the feedback energy and resultant amplification serve to increase the response for the higher frequencies. By suitable adjustment of the constance of the condenser ID, the inductance II, and the feedback condenser 8, the amount of energy returned to the grid circuit can always be kept below the point at which sustained oscillations take place.

Accordingly, therefore, a uniform response of:

frequency, which serves to control the brilliance of the incoming wave, is readily obtainable. It will be appreciated that the constants may be so adjusted that instead of obtaining uniform amplification for the range of frequencies, the higher frequencies can be made to predominate or be subordinate to those of the incoming signals which serve to feed impulses to the tube 1 by way of the winding 6. Where it is desirable to increase'the range over which frequencies desired to be reproduced can be controlled, a plurality of differently tunable circuits 9 may be provided. It will thus be appreciated that the essential steps in accomplishing applicants invention is to detect the signal, utilize the fundamental frequency of the detected signal to produce sharp impulses at a frequency corresponding to the received detected signal, deriving a series of damped oscillations, and controlling the amplitude response of the damped oscillations to provide the final signal to actuate the sound reproducer.

Other features of the outfit up to the loudspeaker or sound reproducer are the same as in audio frequency amplifier circuit schemes. In a similar way amplifiers may be designed which are adepted to be controlled from sound records made in accordance with this invention by electro-magnetic or photo-electric ways and means, such as any well known type of sound-film.

Having now described our invention, what we claim and desire to secure by Letters Patent is the following:

1. A system of sound production which coinprises means for receiving signals representative of fundamental sound frequencies, a local oscillater means for producing a train of damped oscillations having a group frequency and a valve frequency, tunable means for controlling the group frequency of the clamped oscillations in accordance with the received signals, ancl lnductance and capacity means for independently ad lusting the damping and wave frequency 2. In a sound producing system, a relaxation oscillator for locally producing damped waves having a group frequency and a, wave frequency, means for receiving signals representative of fundamental souncl frequencies, means for ceusthe received signals to modify the group ire quency of the locally produced damped waves, a circuit including capacity anal inductance elements for controlling the damping; and Wave frequency of the resulting group frequencies.

8. The method of controlling the timbre of re oelved sound signals, comprising the steps of proelucing a train of audio electrical signal energy, producing relaxation oscillations, controlling said produced, oscillation by said produced signal energy, amplifying said controlled oscillations, controlling the damping of said amplified osoilla-= lions, and. converting said resultant oscillations into audible energy.

GEORG voN ARGO.

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